1. Field of the Invention
The present invention relates to a synthetic resin cage for a roller bearing.
2. Description of the Related Art
Conventionally, a synthetic resin cage for a roller bearing includes a cylindrical body made of a synthetic resin. A number of pockets for accommodating respective rollers are formed in the cylindrical body and arranged in the circumferential direction of the cylindrical body at predetermined intervals. A columnar portion is formed in the cylindrical body so as to separate adjacent pockets from each other. In other words, in the cage, two annular bodies axially separated from each other are integrally connected by a number of columnar portions arranged in the circumferential direction of the cage at predetermined intervals. Each pocket is defined by the opposite annular bodies and the adjacent columnar portions.
FIG. 3 shows an example of such a conventional synthetic resin cage for a roller bearing (see Japanese Patent Application Laid-Open (kokai) No. 9-79268).
In the cage 1 of FIG. 3, a radially outer surface of a columnar portion 3 is a portion of a cylindrical surface which is in parallel with the outer circumferential surface of a cylindrical body of the cage 1. A radially inner surface 5 of the columnar portion 3 is a portion of the inner circumferential surface of the cylindrical body. Circumferentially opposite side surfaces of the columnar portion 3 extend along the axial direction of the cage 1 and are substantially in parallel with the radial centerlines of the corresponding pockets (see FIG. 2).
Axially opposite end regions 20 of the radially outer surface of the columnar portion 3 adjacent to respective annular bodies 4 are portions of a cylindrical surface whose radius is appropriately smaller than that of the outer circumferential surface of the cylindrical body, or that of the outer circumferential surfaces of the annular bodies 4. The outer circumferential surfaces of the annular bodies 4 serve as guide surfaces for the cage 1. A central region 21 of the radially outer surface of the columnar portion 3 located between the axially opposite end regions 20 is a portion of a cylindrical surface whose radius is appropriately smaller than that of the axially opposite end regions 20, and serves as a surface of a passageway for lubrication oil.
Grooved portions 7 are formed in the circumferentially opposite side surfaces of the columnar portion 3 at axially opposite end regions, which correspond to the axially opposite end regions 20. Accordingly, the thickness of the columnar portion 3 as measured circumferentially at the grooved portions 7 is thinner than that as measured at the other regions of the columnar portion 3.
Auxiliary roller-retaining portions 22 are formed on either circumferential edge of the radially outer surface of the columnar portion 3 at axially opposite end portions of the central region 21 in such a manner as to project toward the pocket. An outer roller-retaining portion 23 is formed on either circumferential edge of the radially outer surface of the columnar portion 3 in such a manner as to be located between and axially separated from the auxiliary roller-retaining portions 22 by an appropriate distance.
The outer roller-retaining portion 23 projects toward the pocket and radially outward and projects more than do the auxiliary roller-retaining portions 22.
An inner roller-retaining portion 24 is formed on either circumferential edge of the radially inner surface of the columnar portion 3 in such a manner as to project toward the pocket and to extend between the grooved portions 7. The inner roller-retaining portion 24 projects less than does the outer roller-retaining portion 23.
The roller bearing of FIG. 3 supports a gear G on a shaft S such that the gear G is rotatable about the shaft S. In the roller bearing, each roller R is accommodated within a respective pocket of the cage 1. The shaft S is fitted into a hole defined by the thus-annularly-arranged rollers R, which, in turn, are fitted into a shaft hole D of the gear G.
A lubrication oil feed hole P is formed in the shaft S along its axis and communicates with an oil discharge hole Q which opens onto the exterior of the shaft S at an axially center position of the cage 1.
Next will be described a flow of lubrication oil within the roller bearing during rotation of the gear G about the shaft S.
Lubrication oil is fed from external lubrication oil feed means into the lubrication oil feed hole P formed in the shaft S. The thus-fed lubrication oil is discharged to the interior side of the roller bearing through the oil discharge hole Q by virtue of a centrifugal force.
Thus, the lubrication oil is fed onto the circumferential surface of each roller R which is rolling on the surface of the shaft S. Due to blockage by the inner roller-retaining portion 24, the lubrication oil flows into each pocket making a detour via the grooved portions 7 located at the axially opposite sides of the inner roller-retaining portion 24, and reaches the central region 21 of the radially outer surface of the columnar portion 3 and then the shaft hole D of the gear G. After lubricating the surface of the shaft S, the circumferential surface of each roller R, and the shaft hole D of the rotating gear G, the lubrication oil flows out to the exterior of the roller bearing through gaps between the outer circumferential surfaces of the annular bodies 4 and the surface of the shaft hole D.
As described above, in the conventional synthetic resin cage for a roller bearing, lubrication oil fed from the external lubrication oil feed means flows into the interior side of the roller bearing via the lubrication oil feed hole P and the oil discharge hole Q of the shaft S. Within the roller bearing, due to blockage by the inner roller-retaining portion 24, the lubrication oil flows into each pocket making a detour via the grooved portions 7 located at the axially opposite sides of the inner roller-retaining portion 24, and reaches the central region 21 of the radially outer surface of the columnar portion 3 and then the shaft hole D of the gear G. After reaching the central region 21 of the radially outer surface of the columnar portion 3, the lubrication oil flows into gaps which are formed at the opposite end regions 20 and which are narrower than the gap formed at the central region 21. The lubrication oil then flows out to the exterior of the roller bearing through the gaps between the outer circumferential surfaces of the annular bodies 4 and the surface of the shaft hole D.
Accordingly, the flow of the lubrication oil within the roller bearing is not smooth. As a result, wear particles and dust which has entered into the roller bearing are not sufficiently discharged to the exterior of the roller bearing. Thus, such a roller bearing raises a problem when applied to gears and like components of construction and agricultural machinery used in dusty environments.